In recent years, miniaturization, weight reduction, multi-functionalization, and so on of electronic devices are much advanced. Following this, LSI (large scale integration) and high integration of chip components, etc. are advanced, and forms thereof are rapidly changed to a multi-pin or miniaturized form. For this reason, in order to improve a mounting density of electronic devices, the development of fine wiring of multi-layered printed wiring boards is advanced. As the multi-layered printed wiring boards which are in agreement with these demands, multi-layered printed wiring boards having a build-up structure using a glass cloth-free insulating resin film as an insulating layer (hereinafter also referred to as “build-up layer”) in place of a prepreg are becoming the main current as a printed wiring board suited for miniaturization, weight reduction, and microfabrication.
As for the build-up layer, in order to improve the processing dimensional stability and also to reduce the amount of warpage after mounting a semiconductor, reduction in thermal expansion is demanded. As one of methods of reducing the thermal expansion of the build-up layer, a method in which a filler is highly filled is exemplified. For example, by incorporating a silica filler in an amount of 40% by mass or more in the build-up layer, it is contemplated to reduce the thermal expansion of the build-up layer (see PTLs. 1 to 3).
Meanwhile, in recent years, computers and information and communication equipment are towards high performance and high functionality more and more, and in order to process a large quantity of data at a high speed, processed signals tend to become higher in frequency. In particular, as for a frequency domain of radio waves used for mobile phones and satellite broadcasting, a high-frequency domain of a GHz band is used. In order to suppress a transmission loss to be caused due to high frequency, as organic materials to be used in a high-frequency domain, materials with low dielectric constant and dielectric tangent are desired.
In response to this, various grappling approaches have been taken. For example, PTL 4 discloses a resin composition containing a cyanate resin.